LinkedBlockingQueue是一个单向链表实现的阻塞队列。该队列按 FIFO（先进先出）排序元素，新元素插入到队列的尾部，并且队列获取操作会获得位于队列头部的元素。链接队列的吞吐量通常要高于基于数组的队列，但是在大多数并发应用程序中，其可预知的性能要低。
此外，LinkedBlockingQueue还是可选容量的(防止过度膨胀)，即可以指定队列的容量。如果不指定，默认容量大小等于Integer.MAX_VALUE。
看一下LinkedBlockingQueue类中定义的重要变量和Node节点，如下：
// 链表的节点定义
static class Node
{
E item;
Node
next; Node(E x) { item = x; } } private final int capacity; // 链表的容量，可以在创建链表时指定 private final AtomicInteger count = new AtomicInteger(0);// 记录队列元素个数 private transient Node
head; // 链表的表头。取出数据时，都是从表头head处插入 private transient Node
last; // 链表的表尾。新增数据时，都是从表尾last处插入 // putLock是插入锁，takeLock是取出锁；notEmpty是非空条件，notFull是未满条件。通过它们对链表进行并发控制 private final ReentrantLock takeLock = new ReentrantLock(); private final Condition notEmpty = takeLock.newCondition(); private final ReentrantLock putLock = new ReentrantLock(); private final Condition notFull = putLock.newCondition();
看一下主要的两个构造函数，如下：
public LinkedBlockingQueue(int capacity) {
if (capacity <= 0) throw new IllegalArgumentException();
this.capacity = capacity;
last = head = new Node
(null);
}
public LinkedBlockingQueue(Collection
c) {
this(Integer.MAX_VALUE);
final ReentrantLock putLock = this.putLock;
putLock.lock(); // Never contended, but necessary for visibility
try {
int n = 0;
for (E e : c) {
if (e == null)
throw new NullPointerException();
if (n == capacity)
throw new IllegalStateException("Queue full");
enqueue(new Node
(e)); ++n; } count.set(n); } finally { putLock.unlock(); } }
将c容器中的元素做为Node节点的值添加到链表中，如下：
private void enqueue(Nodenode) { // assert putLock.isHeldByCurrentThread(); // assert last.next == null; last = last.next = node; }
将node节点添加到last.next节点后面，并将last.next节点的值赋给last.
public void put(E e) throws InterruptedException {
if (e == null) throw new NullPointerException();
// Note: convention in all put/take/etc is to preset local var
// holding count negative to indicate failure unless set.
int c = -1;
Node
node = new Node(e);
final ReentrantLock putLock = this.putLock;
final AtomicInteger count = this.count;
putLock.lockInterruptibly();
try {
/*
* Note that count is used in wait guard even though it is
* not protected by lock. This works because count can
* only decrease at this point (all other puts are shut
* out by lock), and we (or some other waiting put) are
* signalled if it ever changes from capacity. Similarly
* for all other uses of count in other wait guards.
*/
while (count.get() == capacity) {
notFull.await();
}
enqueue(node);
c = count.getAndIncrement();
if (c + 1 < capacity)
notFull.signal();
} finally {
putLock.unlock();
}
if (c == 0)
signalNotEmpty();
}
/**
* Inserts the specified element at the tail of this queue, waiting if
* necessary up to the specified wait time for space to become available.
*/
public boolean offer(E e, long timeout, TimeUnit unit)
throws InterruptedException {
if (e == null) throw new NullPointerException();
long nanos = unit.toNanos(timeout);
int c = -1;
final ReentrantLock putLock = this.putLock;
final AtomicInteger count = this.count;
putLock.lockInterruptibly();
try {
while (count.get() == capacity) {
if (nanos <= 0)
return false;
nanos = notFull.awaitNanos(nanos);
}
enqueue(new Node
(e)); c = count.getAndIncrement(); if (c + 1 < capacity) notFull.signal(); } finally { putLock.unlock(); } if (c == 0) signalNotEmpty(); return true; } /** * Inserts the specified element at the tail of this queue if it is * possible to do so immediately without exceeding the queue's capacity, */ public boolean offer(E e) { if (e == null) throw new NullPointerException(); final AtomicInteger count = this.count; if (count.get() == capacity) return false; int c = -1; Node
node = new Node(e); final ReentrantLock putLock = this.putLock; putLock.lock(); try { if (count.get() < capacity) { enqueue(node); c = count.getAndIncrement(); if (c + 1 < capacity) notFull.signal(); } } finally { putLock.unlock(); } if (c == 0) signalNotEmpty(); return c >= 0; }
2、删除元素
public boolean remove(Object o) {
if (o == null) return false;
fullyLock();
try {
for (Node
trail = head, p = trail.next;
p != null;
trail = p, p = p.next) {
if (o.equals(p.item)) {
unlink(p, trail);
return true;
}
}
return false;
} finally {
fullyUnlock();
}
}
public E take() throws InterruptedException {
E x;
int c = -1;
final AtomicInteger count = this.count;
final ReentrantLock takeLock = this.takeLock;
takeLock.lockInterruptibly();
try {
while (count.get() == 0) {
notEmpty.await();
}
x = dequeue();
c = count.getAndDecrement();
if (c > 1)
notEmpty.signal();
} finally {
takeLock.unlock();
}
if (c == capacity)
signalNotFull();
return x;
}
public E poll(long timeout, TimeUnit unit) throws InterruptedException {
E x = null;
int c = -1;
long nanos = unit